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highly coloured for direct titration, the ether is distilled off, the residue
treated with 20 c.c. of hot alcohol and the acidity of the alcoholic liquid
determined. Examination of the aqueous hydrochloric solution will indicate
the base present in the soap.

7. Resin Oils.—i. DETECTION. Resin oils are detected by their
odour and by Morawski's reaction, which consists in treating a small quantity
of the oil in a test-tube with acetic anhydride and adding a drop of sulphuric
acid (D 1-53) : the appearance of a transient violet coloration indicates the
presence of resin oil.

Resin oils may be detected also by shaking the oil (freed, if necessary,
from saponifiable matter) with an equal volurre of acetone and allowing
the two liquids to separate, the acetone containing very little mineral oil
and almost the whole of the resin oil. If the solvent is evaporated, the
resin oil in the residue may be characterised by the red coloration which
it imparts to an equal volume of sulphuric acid (D 1-6), by its high specific
gravity (0-970-0-980) and by its rotatory power.

2. DETERMINATION. Storch's method is used: 10 grams of the oil
(freed from saponifiable matters when these are present) are treated in a
flask, at a gentle heat and with shaking, with 50 grams of 96% alcohol.
After cooling, the alcoholic liquid is transferred to a weighed beaker and
the oily liquid washed with a little alcohol, which is also added to the beaker.
The alcohol is evaporated on the water-bath and the residue weighed (A}.
This residue is treated again with alcohol (10 times its weight), evaporation
of the alcoholic solution giving a new residue (B). The mineral oil present

in this residue is calculated by means of the formula,--------~~, where A

(a - b}

and £ are the weights of the two residues and a and b the quantities of
alcohol used in their treatment. Subtraction of the calculated weight of
mineral oil from B gives the quantity of resin oil.

EXAMPLE : 10 grams of oil, treated with 50 grains of alcohol, gave a residue
of 1-51 gram (A), and this, treated with 15-1 grams of alcohol, gave a residue,
1-15 gram (B). From the proportion

50-15-1 : 1-51-1-15 = 15-1 : x,

x = 0-155. Amount of resin oil in 10 grams of the oil taken = 1-15 — 0-155 =
0-995 gram.

8.  Tar Oils.—The presence of tar oils is recognised besides, by their
characteristic odour, by the property they exhibit of reacting energetically
with nitric acid (D 1-45) giving nitro-derivatives, by their solubility in
cone, sulphuric acid on a water-bath with formation of compounds soluble
in water, and by the general reactions of the phenols (see Tar Oils, Car-
bolic Acid).

9.  Defluorescent and  Odoriferous  Substances.—To  destroy the
fluorescence of heavy oils, a-nitronaphthalene is usually employed, while
the unpleasant fatty smell is masked by addition of nitrobenzene.   The
latter is readily detected by the odour of bitter almonds it imparts to the
oil, whilst the odourless nitronaphthalene is recognised as follows : Holde
proposes a preliminary test by heating 1-2 c.c. of the oil for a short time added and the acidity determined, the fatty acids being deduced from